1. Field of Invention
This invention relates to radio telemetry, and more particularly to systems and methods for transmitting sensor information to a user""s location remote from the sensor.
2. Description of Related Art
A typical radio telemetry system employs one of several different modulation methods, and one of several different multiplexing techniques, in order to transmit information produced by multiple sensors to a user""s location remote from the sensors. Well known methods of modulating a carrier frequency to convey information include amplitude modulation, frequency modulation, phase modulation, and pulse modulation. Well known multiplexing methods include frequency division multiplexing and time division multiplexing.
Known pulse modulation techniques include pulse amplitude modulation, pulse code modulation, pulse frequency modulation, and pulse width modulation. In pulse amplitude modulation (PAM), the amplitude of a pulse corresponds to that of a modulating waveform. In pulse code modulation, PAM pulses are sampled at regular intervals and quantized (i.e., assigned a digital value). In pulse frequency modulation, pulses of equal amplitude are generated at a rate determined by the amplitude of the modulating waveform. In pulse width modulation, pulses are generated at a regular rate, and the widths of the pulses are determined by the amplitude of the modulating waveform.
In the United States, the Federal Communications Commission (FCC) regulates radio communications. The FCC has set aside certain frequencies for the radio control (R/C) radio service. R/C is for one-way, short distance, non-voice radio service for: (i) allowing an operator to turn on or off a device at a remote location, or (ii) turning on or off an indicating device for the operator by a sensor at a remote location. The fact that there are no age or citizenship requirements to operate for an R/C unit, and license documents are neither required nor issued, makes R/C communications attractive.
Both regulatory and practical limitations bear upon the lengths of R/C communications. According to 47 C.F.R. 95.215 (R/C Rule 15), the lengths of R/C communications must be limited to xe2x80x9cthe minimum practical time.xe2x80x9d On the practical side, the lifetimes of batteries powering R/C transmitters decrease with increasing lengths of R/C communications.
It would thus be desirable to have a system and method for radio telemetry suited for R/C communications. The system and method would also preferably minimize the lengths of radio communications.
A telemetry system is described, including a remote unit having a remote input unit coupled to a remote transmit unit. The remote input unit receives one or more sensor output signals and produces a sensor status signal dependent upon the sensor output signals. The sensor status signal alternates between a first state and a second state, wherein an amount of time the sensor status signal remains in the first state is dependent upon one of the sensor output signals. The remote transmit unit receives the sensor status signal and transmits a transmit signal each time the sensor status signal transitions between the first and second states.
The sensor output signal used to determine the amount of time the sensor status signal remains in the first state may be an analog signal produced by a sensor (e.g., and analog sensor) in response to an input measurand (e.g., temperature, pressure, humidity, wind speed, wind direction, or a level of collected rain water).
The transmit signal may be a frequency modulated radio frequency carrier signal. In one embodiment, the transmit signal has a status portion including direction information indicating a direction of the transition between the first and second states (e.g., xe2x80x981xe2x80x99 for a transition from the second state to the first state, and xe2x80x980xe2x80x99 for a transition from the first state to the second state). The transmit signal may also have an identification portion including identification information uniquely identifying the remote unit.
The telemetry system may also include a base unit coupled to receive the transmit signals transmitted by the remote transmit unit, wherein the base unit is configured to reproduce the sensor status signal from the transmit signals. The base unit may also produce a sensor status from the sensor status signal, and may display the sensor status.
In one embodiment, the remote input unit receives a first sensor output signal from a first sensor and a second sensor output signal from a second sensor. The first sensor may be an analog sensor, and the first sensor output signal may be an analog signal produced by the analog sensor in response to an input measurand (e.g., temperature, pressure, humidity, wind direction, wind velocity, and a level of collected rain water). The second sensor may be a digital sensor, and the second sensor output signal may be a digital signal produced by the digital sensor. The remote input unit produces the sensor status signal dependent upon the first and second sensor output signals such that: (i) the amount of time the sensor status signal remains in the first state is dependent upon the first sensor output signal, and (ii) an amount of time the sensor status signal remains in the second state is dependent upon the second sensor output signal.
A method for conveying sensor status information includes receiving a sensor output signal, and producing a sensor status signal depending upon the sensor output signal, wherein: (i) the sensor status signal alternates between a first state and a second state, and (ii) an amount of time the sensor status signal remains in the first state is dependent upon the analog sensor output signal. A transmit signal is broadcast each time the sensor status signal transitions between the first and second states, wherein the transmit signal includes direction information indicating the direction of the transition between the first and second states.
The receiving step may include receiving a first sensor output signal (e.g., an analog signal produced by an analog sensor) and a second sensor output signal (e.g., a digital signal produced by a digital sensor). The sensor status signal may be produced depending upon the first and second sensor output signals, wherein: (i) the amount of time the sensor status signal remains in the first state is dependent upon the first sensor output signal, and (ii) an amount of time the sensor status signal remains in the second state is dependent upon the second sensor output signal.